1. Field of the Invention
The present invention relates to an apparatus and method for controlling multicast and broadcast information. More particularly, the present invention relates to an apparatus and method for transmitting control information for a multicast and broadcast service.
2. Description of the Related Art
Mobile stations were originally developed to provide simple wireless communication between users. As technology has advanced, mobile stations now provide many additional and advanced features beyond the simple telephone conversation. One advanced feature is the provision of multimedia entertainment.
To provide multimedia entertainment on a mobile station, much higher data rates are required as compared to those needed for providing a voice service or even for providing a Short Messaging Service (SMS). To address the provision of multimedia entertainment in the next generation wireless systems, different standards bodies have assigned specific services for this task. For example, in the 3rd Generation Partnership Project (3GPP) standard, the multimedia content is carried on a Multimedia Broadcast and Multicast Service (MBMS). In 3GPP2, it is carried on a Broadcast and Multicast Service (BCMCS), and in the Institute of Electrical and Electronics Engineers' (IEEE) Air Interface for Fixed Broadband Wireless Access Systems 802.16 standard, it is carried on a Multicast and Broadcast Service (MBS).
The body of IEEE 802.16 standards includes the 802.16e standard, and the 802.16m standard, which is currently under development to enhance the 802.16e standard. Accordingly, the enhancements to the MBS in the 802.16m standard are termed “Enhanced-MBS” (E-MBS). In the IEEE 802.16e standard, control signaling for MBS is transmitted as an MBS MAP message. The MBS MAP message conveys information required to decode an MBS data burst of the service to which a user subscribes and may include control signaling to decode MBS data bursts for various subscriptions. Information necessary for decoding all MBS data bursts in an MBS zone will be transmitted in the MBS MAP. Consequently, the MBS MAP will contain as many Information Elements (IEs) as the number of services offered. Each MBS service is identified by a unique combination of Station ID (STID) and Flow ID (FID). To accommodate different transmission scenarios, different types of IEs have been defined by the IEEE 802.16 standard. More particularly, the IEs are categorized into MBS_DATA_IE, MBS_DATA_Time_Diversity_IE and Extended_MBS_DATA_IE. Depending on the transmission scenario for the MCIDs in the zone, the MBS MAP may contain some or all of the IEs.
FIG. 1 illustrates a Frame configuration according to the related art.
In the proposed IEEE 802.16m standard, E-MBS is a downlink transmission from a Base Station (BS) to one or more Mobile Stations (MSs) subscribing to the service. The downlink of the IEEE 802.16m standard uses an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme for transmission to the MSs. OFDM is a multi-carrier technique where the available bandwidth is split into many small bands known as subcarriers using simple Inverse Fast Fourier Transform/Fast Fourier Transform (IFFT/FFT) operations, wherein the subcarriers' bandwidths are the same. Subcarriers are used to carry either control signaling or data for MSs. An OFDM symbol is a collection of subcarriers that span the system bandwidth. Further, to make resource utilization more efficient, OFDM symbols are grouped to form a sub-frame. In the IEEE 802.16m standard and as illustrated in FIG. 1, 6 OFDM symbols 101 are used to form a regular sub-frame 103 that is 0.625 ms long, 8 such regular sub-frames form a frame 105 that is 5 ms long, and 4 frames form a Super Frame 107 that spans 20 ms.
An E-MBS Scheduling Interval (MSI) is currently defined in the IEEE 802.16m-08/003r6 draft System Description Document (SDD). The E-MBS MSI refers to a number of successive frames for which the access network may schedule traffic for the streams associated with the E-MBS prior to the start of the interval. The length of this interval depends on the particular use case of the E-MBS and is dictated by the minimum switching time requirement that is set in the IEEE 802.16m-08/002r7 System Requirements Document (SRD). In other words, MSI refers to the transmission frequency of a particular E-MBS stream and thus the frequency at which the E-MBS MAP is transmitted. Additionally, the SDD mentions that the E-MBS MAP message may be structured such that it efficiently defines multiple transmission instances for a given stream within an MSI. It is also worth noting that in the sub-frames in which the E-MBS MAP is transmitted, it is transmitted in the first few resource units reserved for E-MBS. The resource units reserved for E-MBS are transmitted in the broadcast channel called the Super Frame Header (SFH).
The E-MBS MAP is transmitted once at the beginning of the MSI and carries with it all the required control information to decode the scheduled traffic over the duration of the MSI. Therefore, the E-MBS MAP is not transmitted in all Super Frames but once every few Super Frames as defined by the MSI. Further, while the duration of the MSI can change over time, the change is not indicated to the MS. Hence, when an MS attempts to receive the E-MBS, it must blindly decode each sub-frame carrying E-MBS data until it can decode the E-MBS MAP. The blind decoding by the MS unnecessarily consumes power and resources.
Accordingly, there is a need for an improved apparatus and method for transmitting control information regarding the transmission of E-MBS MAP.